1. Field of the Invention
This invention relates to color imaging systems and methods. In particular, this invention is related to systems and methods of separating different light into two or more spectrums, modulating the separated spectrums, and re-combining the modulated spectrums to create color images.
2. Background of the Related Art
Some prior art color image projector systems separate input light into three primary colors, separately modulate the colors, and recombine the modulated color images to create a consolidated, modulated color image. Prior art systems typically separate input white light into multiple colors using multiple dichroic beamsplitters. Usually, a first dichroic beamsplitter will separate the white light into a first primary color, and a complementary color. The complementary color light is then further separated into second and third primary colors by a second dichroic beamsplitter. Once the white light has been separated into three primary color beams, the light beams are separately modulated. Additional dichroic elements are then used to re-combine the modulated beams.
The dichroic beamsplitters used in these prior art systems typically use a thin film of a dichroic material that is deposited on a transparent substrate, or sandwiched between two shaped transparent elements. Unfortunately, the performance of the dichroic thin film material is poor off-axis. Thus, the performance of devices using the dichroic beamsplitters is usually poor off-axis.
The dichroic thin films used in the prior art systems are intended to act on light based only on wavelength. The polarization orientation of the light passing through the dichroic elements should not matter, and the dichroic elements should not change the polarization orientation of the light. In practice, however, the polarization orientation of the light does have an effect on how the dichroic thin films affect the light.
If a prior art system utilizes liquid crystal modulators, the light may be polarized into specific orientations to allow the modulators to perform their function. This polarization orientation can affect how the dichroic thin films perform the color separation function. In addition, if the liquid crystal modulators are reflective panels, the colored light will usually pass through a dichroic thin film a first time with a first polarization orientation, and then a second time with a different polarization orientation. Because the polarization orientation changes, the dichroic thin film will operate on the light differently during each pass. All these effects combine to deteriorate the performance of the prior art systems.
In addition, to improve color saturation, many of the prior art devices that utilize dichroic beamsplitters to separate light into three primary colors also utilize notch or band-pass filters to remove light having wavelengths between the three primary colors. For instance, notch filters are often used to remove cyan and yellow "pastel" colors. The removal of the pastel colored light reduces the brightness of the resulting color images.